Jerry and Rita Alter kept to themselves. They were a lovely couple, neighbors in the small New Mexico town of Cliff would later tell reporters. But no one knew much about them. They may have been hiding a decades-old secret, pieces of which are now just emerging. Among them: After the couple died, a stolen Willem de Kooning painting with an estimated worth of $160 million was discovered in their bedroom. More than 30 years ago, that same painting disappeared the day after Thanksgiving from the University of Arizona Museum of Art in Tucson. And Wednesday, the Arizona Republic reported...